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We investigated the direction distribution of protons around 20 km of altitude by mean of stratospheric balloons. Our detection instrument was based on two large silicon diodes, which were differently tilted. Our measurements show that the proton flux is not isotropic and that protons have a higher probability to have a direction near the vertical axis than near the horizontal axis which proved the proton flux anisotropy. By simulation we then determined an empirical expression for the angular differential fluence of protons.